Newtron (メレオン,Mereon?) is a chameleon-type Badnik created by Dr. Eggman. It makes its first appearance in original 16-bit version of Sonic the Hedgehog. There usually exist two types in the games, as both types of Newtrons are one of a handful of Badniks which exhibit a cloaking ability.
Sonic the Hedgehog (1991)
Newtron makes its first appearance in the original 16-bit version of Sonic the Hedgehog as the Badnik that has two variations at Green Hill Zone. Both of them can be destroyed with Spin Jump as it starts to appear on the wall. Green variants might be shooting energy balls from bottom walls, which the player has to avoid. During some occasions, the player is unable to destroy green variants of Newtron Badniks depending on their placement in the Zone.
In 8-bit version of the game with same name, only the green variation of Newtrons appear at Jungle Zone, but do have the same attack patterns like they do in their 16-bit counterpart. However Newtrons don't have animal friends inside of them as power source like many other Badniks in Master System and Game Gear titles.
Sonic the Hedgehog 2
Newtron also makes appearance as common enemies in 8-bit version of Sonic the Hedgehog 2, as these Badniks are featured at Under Ground Zone, Sky High Zone and Green Hills Zone. This game also has two variations of Newtrons, although green one is more grayer here. Both types have same attack patterns from previous game, although none of them don't include animal friend.
Sonic the Hedgehog 4
Newtron reappears in Sonic the Hedgehog 4: Episode I in Splash Hill Zone. In the game, only the green variety appears. It keeps its attack pattern from the first appearance, but it has an extra attack where it transforms itself as a missile which starts moving in a side direction along the platform.
Sonic 4 Website info
Newtron surprises Sonic again using optical camouflage to try and blast Sonic. He can also transform into a rocket and charge towards Sonic.
Newtron reappears in Nintendo 3DS version of Sonic Generations. Both the blue and the green varieties are featured in Green Hill. Despite having redesign in the game, both types of Newtron have the same attack pattern as from their first appearance and are placed exact same places in classic Sonic's act.
Sonic Lost World
Green variants of Newtrons appeared in Sonic Lost World, where these Badniks are featured at Windy Hill. During the game, it turns out that Badniks, Newtrons included, got hijacked by the Deadly Six. While having a cartoon-like appearance from earlier installments once again, these Badniks mostly have similar patterns, as they are hanging on walls and shooting projectiles toward the player. These Badniks will again also contain animals inside of them.
Newtron as a Badnik is based on a chameleon. A Newtron body has a head, stripy tail and four white feet, which each of them has three fingers. One of fingers stretches in the other direction, so the Newtron can hold extract. A Newtron has yellow eyes with small pupils, brown sharp parietal crest. Newtrons come in two varieties: green and blue. The green variation has yellow eyes and the blue has red eyes.
Both green and blue varieties hide camouflaged inside a wall and phase out of hiding when they see Sonic, but they have different methods of attack:
The green Newtron, after becoming visible, spits a ball of energy at Sonic. It then phases back into its surroundings. It never moves outside of its wall, so it's technically invincible.
The blue Newtron doesn't stay in one place or fire energy balls. After becoming visible, it moves out of the wall and drops to the ground, chasing Sonic in a fixed horizontal line. The blue variety is easier to deal with as it can be attacked, unlike its green counterpart.
Newtrons have appeared in several early issues of Sonic the Comic as standard members of Doctor Robotnik's Badnik army. Earlier models of Newtrons (which appears to based on the game appearance) appear to be weak and quadruped.
Later Newtron models have completely different patterns as they don't use projectile weapons nor cloaking ability, but simply attacked enemies with their claws, teeth and tails. These Newtrons also appear to stand on two legs. These Newtrons are more bipedal and serve as melee fighters of the Badnik army. However these models got decommissioned after the electromagnetic pulse, which affected the Mobius.
Newtron makes few appearances in Archie's Sonic the Hedgehog comics as part of Robotnik's Badniks. Newtron along with Ballhog are seen as setting the explosion to blowing up a unnamed place as attempting to flush out a spy, but bomb early explodes, because of Sonic who knew this and set them off before the bomb could reach its intended target. The Newtron was part of Badnik team, which consisted him, Coconuts, Crabmeat, Buzz Bomber, Slicer and Roller to break up the apparent wedding of Sonic the Hedgehog and Sally Acorn. Despite their assault, Newtron got easily defeated as other Badniks in team while the wedding reveals to be just playing.
Years later Newtron appears in the Genesis-story arc in Sonic the Hedgehog comic bookSonic the Hedgehog #226. In Green Hill Zone, one of the Newtrons loomed Sonic from behind, but he managed to grab him and headed forward using him as surfboard. After this Sonic let him crash into the Egg Capsule, as both capsule and Badnik gets destroyed.
The toy company TOMY has released Newtron action figurine during the release of Sonic & Knuckles as it also includes a series of 21 Sonic figurines and these figurines came in packs of four under the Sonic & Knuckles label and were also released individually under a Sonic the Hedgehog label.